This invention relates to a siloxane-based tintable coating composition for forming abrasion-resistant coatings on lenses or other optical articles, especially those formed from synthetic plastics.
In recent years, synthetic plastics such as polycarbonate have replaced glass in many optical applications, particularly opthalmic lenses, because of the lighter weight and superior impact resistance of the plastics. However, plastics such as polycarbonate are relatively soft, and must receive an abrasion-resistant coating to provide an acceptable level of abrasion or scratch resistance. Many abrasion-resistant coating compositions of the prior art are of the polysiloxane type, in which crosslinking is provided by condensation of silane groups formed by hydrolysis of alkoxysilanes. Representative compositions of this type are disclosed in Treadway et al U.S. Pat. No. 4,378,250 and the references cited therein. Although the compositions disclosed in these references are useful in the formation of abrasion-resistant coatings, considerable room for improvement remains in terms of abrasion resistance and tintability.